Cardiopulmonary resuscitation (CPR) is widely used in clinical medicine to maintain perfusion of vital organs during episodes of sudden cardiac arrest when the heart stops spontaneously beating (asystole). Any period of prolonged asystole (such as from ventricular fibrillation) can cause irreversible hypoxic damage to vital end organs (such as the brain and heart) that are not perfused during the asystolic episode. CPR can often maintain a sufficient level of arterial oxygenation and blood flow to avoid irreversible end organ damage and death, at least until spontaneous cardiac activity resumes or external ventricular defibrillation converts the cardiac rhythm to a more effective electrocardiographic pattern.
The components of CPR usually include external cardiac compressions and pulmonary ventilation. The external cardiac compressions are achieved by repetitively forcing the sternum against the heart to compress the heart between the sternum and vertebral column. Manual chest compressions also produce a positive intrathoracic pressure and enhance emptying of the heart, possibly by reducing afterload of the left ventricle. Cardiac compressions are usually only interrupted to administer mouth-to-mouth or mechanical ventilation, which cyclically inflates the lungs to achieve oxygenation of the blood, or to attempt electrical cardioversion of the fibrillating heart.
Although CPR has improved initial survival of episodes of sudden cardiac death, its effectiveness is less than optimal. External compression of the heart, for example, is not as effective as surgically opening the chest and performing direct manual compression of the heart. Several studies have estimated that in-hospital CPR is effective in only 10-15% of patients. Open chest cardiac massage can better achieve normal or supranormal cerebral blood flows, which are associated with improved neurologic recovery from the cardiac event. Such dramatic surgical intervention is not usually available, however, and even in a hospital setting is often impractical or not feasible. The inability of closed chest CPR to maintain adequate levels of cerebral blood flow is the principal reason for the low survival rates and poor neurologic recovery often associated with CPR. Moreover, external chest compressions frequently cause significant morbidity, such as broken ribs or a fractured sternum.
Both external (closed chest) and surgical (open-chest) techniques of cardiac compression can be performed manually, or with the aid of mechanical devices. With either technique, the goal is to maintain artificial circulation, including perfusion of cerebral and coronary arteries, until spontaneous cardiac activity can be restored. An example of an intrathoracic cardiac massager is shown in U.S. Pat. No. 3,496,392, which discloses an inflatable bladder for insertion between the sternum and heart. After intrathoracic placement, the inflatable bladder is cyclically inflated and deflated to achieve cardiac compression.
U.S. Pat. No. 3,233,607, U.S. Pat. No. 3,478,737, U.S. Pat. No. 4,536,893, U.S. Pat. No. 5,119,804 and U.S. Pat. No. 5,383,840 all disclose mechanical devices that surround and engage the ventricular regions of the myocardium to provide auxiliary cardiovascular support for impaired myocardium. U.S. Pat. No. 5,385,081 shows a similar device, but the device is placed in the intrapericardial space. U.S. Pat. No. 5,484,391 describes a substernal heart massaging plunger that is surgically inserted through an intercostal space to compress the heart.
Although these and other heart compressing devices effectively achieve arterial perfusion, they require surgical placement that is often unavailable or impractical in emergency outpatient or clinical settings. Moreover, surgical procedures performed under emergency conditions often inadvertently and unavoidably introduce infectious pathogens into the patient, which can frustrate or prevent recovery.
Other devices have been developed to assist with external cardiac compression, and that avoid the necessity of surgical placement. U.S. Pat. Nos. 5,490,820 and 5,453,081, for example, both disclose external, vest-like devices that are worn by a patient to provide external chest compressions that promote movement of blood from the heart.
None of these devices have been able to provide an approach that combines the effectiveness of intrathoracic cardiac compression with the convenience and availability of external compression devices.
Accordingly, it is an object of this invention to provide an apparatus and method that achieves superior cardiac compression during episodes of ineffective cardiac contraction or asystole.
Yet another object is to provide such an apparatus and method that performs cardiac compression without the necessity of surgical intervention.
These and other objects of the invention will be understood more clearly by reference to the following detailed description and drawings.